basic_json::is_discarded¶

constexpr bool is_discarded() const noexcept;

This function returns true if and only if the JSON value was discarded during parsing with a callback function (see parser_callback_t).

Return value¶

true if type is discarded, false otherwise.

Exception safety¶

No-throw guarantee: this member function never throws exceptions.

Complexity¶

Constant.

Notes¶

This function will always be false for JSON values after parsing. That is, discarded values can only occur during parsing, but will be removed when inside a structured value or replaced by null in other cases.

Example¶

Example

The following code exemplifies is_discarded() for all JSON types.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    // create JSON values
    json j_null;
    json j_boolean = true;
    json j_number_integer = 17;
    json j_number_unsigned_integer = 12345678987654321u;
    json j_number_float = 23.42;
    json j_object = {{"one", 1}, {"two", 2}};
    json j_array = {1, 2, 4, 8, 16};
    json j_string = "Hello, world";
    json j_binary = json::binary({1, 2, 3});

    // call is_discarded()
    std::cout << std::boolalpha;
    std::cout << j_null.is_discarded() << '\n';
    std::cout << j_boolean.is_discarded() << '\n';
    std::cout << j_number_integer.is_discarded() << '\n';
    std::cout << j_number_unsigned_integer.is_discarded() << '\n';
    std::cout << j_number_float.is_discarded() << '\n';
    std::cout << j_object.is_discarded() << '\n';
    std::cout << j_array.is_discarded() << '\n';
    std::cout << j_string.is_discarded() << '\n';
    std::cout << j_binary.is_discarded() << '\n';
}

Output:

false
false
false
false
false
false
false
false
false

Version history¶

Added in version 1.0.0.